Allergic reactions to glyceryl trinitrate and isosorbide dinitrate demonstrating cross-sensitivity

Glyceryl trinitrate (nitroglycerin) has been in use for relief of angina for over a hundred years, but allergic reactions to it or to other organic nitrates rarely feature in the medical literature. Most of the case reports describe reactions to transdermally applied nitroglycerin. We report a case of a localized allergic reaction to nitroglycerin transdermal patches that developed when these were worn for the first time after 7 days of uneventful treatment with intravenous isosorbide dinitrate. The reaction evolved into a severe and generalized maculopapular rash with facial swelling when intravenous isosorbide dinitrate was re-administered 10 days later. Subsequent patch testing with a transdermal nitroglycerin patch and a placebo nitroglycerin-free patch provoked a reaction to the nitroglycerin patch but not to the placebo, thus excluding allergy to other constituents of the nitroglycerin patch.